1. Field of the Invention
The invention relates to a novel communication link for permitting communications between cars of a multi-car vehicle such as railway or subway trains. More specifically, the invention relates to such a communication link which includes free space radio communications between adjacent cars of the railroad or subway train.
2. Description of the Prior Art
In order to adapt to changing system requirements, such as passenger or freight volume, routing, maintenance, crew or rolling stock availability, etc., rail cars are coupled and uncoupled frequently. Train configuration and reconfiguration in this sense represents a significant proportion of all train operation, whether considered in terms of rolling-stock-hours, man-hours, out-of-service hours, or whatever. Therefore, these processes must be made as simple and as automated as possible.
While it is true that trains are made up a variety of different types of cars, and in some cases, certain groups of cars are rarely uncoupled, it is nonetheless a fact that a great number of individual couplings and uncouplings are performed every day. An example of a present system is illustrated in U.S. Pat. No. 5,121,410, Demarais, Jun. 9, 1992. As can be seen in FIG. 4 and 5 of the '410 patent, communication lines between cars (car n-1, car n and car n+l) is effected by twisted pairs of wires.
This invention addresses the problem of how to provide adequate information transfer between cars without inhibiting train car coupling or uncoupling.
This invention proposes a solution which provides high-volume, high-reliability information transfer between cars.
Information transfer between devices installed on different cars, in the form of electrical signals, has been a common feature of trains for a number of years. The electrical pathway that carries these signals is called a "trainline". It is made up of a bundle of wires, each of which is connected in an electrically continuous path over the length of the train.
On board devices that use the trainline can interact with each other in a wide variety of ways. For example, a device on one car, such as a switch, may be used to control a number of similar devices, such as lights, on every car of the train. For another example, a specific type of sensor may be installed on every car. If certain conditions arise on one car, the sensor may need to activate a warning buzzer installed in the cab of the head car. Many other configurations are possible.
The changing trainline information transfer requirements brought on by advances in electronic technology over the past two decades have given rise to new problems for trainline designers. Two interrelated factors are at issue here: information volume and information reliability.
In general, the volume of information transferred between rail cars has increased over the period mentioned. It promises to continue to increase for some time to come, as train systems on board each car utilize more and more electronic and electrical equipment. This increased information flow may be addressed in two ways. The increased flow may be handled by an increasing number of wires, or else each wire must handle a larger volume of information.
Reliability of information transfer between cars is and always has been essential to safe, efficient train operation. Within each car, reliability is accomplished by providing mechanically secure conventional electrical connectors that are rarely opened. However, for communications between adjoining cars, the connecting elements on the adjoining cars must be automatically and frequently connected and disconnected, rendering conventional electrical connectors inefficient.
The use of such connecting elements cause many problems leading to a large percentage of subway service interruptions. Some of the problems are as follows:
1. Faulty electrical contact caused by pin oxidation. PA0 2. Faulty electrical contact caused by dirt, grease and foreign matter on pins that accumulates when the pins are disconnected and therefore exposed. PA0 3. Electrical contact is prevented when a pin fails to spring back out to its proper position due to accumulated dirt, grease and foreign matter inside the pin tube. PA0 4. Electrical contact is prevented when returned springs fail due to loss of spring elasticity, which in turn is caused by de-tempering of the spring steel when abnormally high electrical current passes through the spring rather than the electrical shunt.
All of the above problems produce service interruptions and require expensive maintenance. Periodically, the pins must be checked and cleaned to ensure correct operation.
It is also known in the art to use optical arrangements to provide communication links between cars within a subset, and between the subsets of a train, as illustrated in U.S. Pat. No. 4,682,144, Ochiai et al, July 21, 1987. Such a system is illustrated in FIG. 4 of the '144 patent.
The problem with optical systems in the environment of either subway or railroad trains is that the systems are operating in very dirty environments so that the optical couplers will very shortly become dirty themselves. Due to the dirt which will accumulate on the optical couplers, optical transmission is degraded and possibly completely eliminated. Accordingly, the system as illustrated in the '144 patent is not a practical solution to the provision to communication links between the end cars of subsets of a train.
In U.S. Pat. No. 3,994,459, Miller et al, Nov. 30, 1976, a radio system is used to provide communications between a car which is derailed from a train and the remainder of the train. However, the '459 patent does not teach any other communications between the cars of the train using radio signals.
Another factor affecting reliability is the increase in information volume mentioned above. All else being equal, as information volume increases, overall reliability tends to decrease.
In summary, current train communications systems attempt to provide reliability by two methods: coupler pins and cable connectors. While the method of cable connectors between cars provides excellent reliability, it makes coupling and uncoupling the cars a laborious process. On the other hand, although coupler pins provide excellent ease of operation, they require high maintenance to maintain adequate reliability. Coupler pins are sensitive to environmental factors, and other problems. By far the highest incidence of communication failure, especially intermittent failure, occurs due to coupler pin problems.
Increasing the number of wires may work up to a point, but limitations are imposed on this method by a number of factors. Among the most serious of these factors is the problem of large numbers of electrical connections between cars that must be coupled and uncoupled frequently. These connections are at best a trade-off between reliability and automation; as their numbers increase, reliability and/or automation are reduced.
Increasing the volume of information handled by each wire eliminates the necessity of large numbers of electrical connections between cars. However, the high volume of information carried by each wire makes these connections vulnerable to both data loss and increased maintenance, due reliability problems associated with the current state of the art of high-volume information flow through coupler pins.